Add eggplant, cabbage, corn, and okra, if desired, to vegetable mixture. Add enough water to partially cover vegetables. Cover and simmer until all vegetables are tender and mixture is thick and creamy, stirring often and adding more water by 1/4 cupfuls if liquid is too thick, about 15 minutes longer. Season to taste with salt and pepper. Transfer stew to bowl; sprinkle with remaining 1/4 cup green onions and serve.